10-26 Exercise 3: Find roots of a quadratic equation

Question

15.5k views

Write a program to find roots of a quadratic equation

A quadratic equation is a second order equation having a single variable. Any quadratic equation can be represented as where a, b and c are constants ( a can't be 0) and x is unknown variable.

寫一個找二次方程的求根程式

For Example

is a quadratic equation where a, b and c are 2, 5 and 3 respectively.

To calculate the roots of quadratic equation we can use below formula. There are two solutions of a quadratic equation.

使用下列公式:

x = (-b + sqrt(D))/(2*a)
x = (-b - sqrt(D))/(2*a)

where, D = (b*b-4*a*c) is Discriminant (判別式), which differentiate the nature of the roots of quadratic equation.

For the complex result (複數根):

realPart = -b/(2*a);
imaginaryPart =sqrt(-D)/(2*a);

Note: We have used sqrt() function to find square root which is in math.h library.

Example input 1:

1 2 1

Example output 1:

Roots of 1.00x^2 + 2.00x + 1.00 = 0 are real and same
x1 = x2 = -1.00

Example input 2:

1 -3 2

Example output 2:

Roots of 1.00x^2 + -3.00x + 2.00 = 0 are real and different
x1 = 2.00
x2 = 1.00

Example input 3:

1 2 2

Example output 3:

Roots of 1.00x^2 + 2.00x + 2.00 = 0 are complex and different
x1 = -1.00+1.00i
x2 = -1.00-1.00i

[Exercise] Coding (C) - asked Oct 26, 2017 in Chapter 5: Selection Statements by semicolon (5.2k points)
ID: 28934 - Available when: 2017-10-26 18:00 - Due to: Unlimited
reopened Oct 26, 2017 by thopd | 15.5k views

56 Answers

Page:

« prev
1
2
3
4
5
6
next »

112233 · Answer 1 · 2017-11-09 17:27:38

Hidden content!
#include *****   **   *
#include  ** * *  ****  *

int main()
{
   * * ** ** * *  * * **** ** a, b, c, determinant, x1,x2, realPart,   **  *   


    *****  ** * * ***  * ** **  ** **    * %lf ****     *  * *   &b, &c);


*  *    *** *** **** **** *** * = b*b-4*a*c;

 **  *   ***      *  ** ****  **** condition for real and different roots


 * *  * *  *** ** ** * ****** for real and equal roots
*  ** *  * *  ****  **** *** (determinant == 0)
**  * *        ****  * ***  *
* ** **  * *   * * *  ***    ****** *** *** *   * *  * = x2 = -b/(2*a);
* ** *** * *  ***** **  *  * ** ** **  **** **       ***        of %.2fx^2 + %.2fx + %.2f = 0 are real and  *  **** ** a,b,c);
 *  *** ** *******  **     *     *  ** * *   * * ****  *  ** *** * ** **** = x2 =    ****  ** x1);
***  * ***  ***** ****   ** *

* *  *    *   **** * *   *   *   if  ** * > 0)
 *    * ****   ***  *   * *
  *  ***  *  *  **  * * **   sqrt() function returns square root
* *    ** *** * *** * *   * ** **    ** **** *****     *   *  = **  * ****  * * ** *
***  ** ** * ****    *** *   **   * *   * ** * *  * *   =  ** *** *   * **  ***

 *  * **     * *    * ** *   ** ** **  * * **** *  * *   *  ***** *  * *  of %.2fx^2 + %.2fx + %.2f = 0 are real and ** * *****   ****  
*  ** *    **** ** **  ****    **  *****  * *  ** **   * ** *** * *  =  * ** * *  x1);
***     **  * **    *   * *** *     * ** * **   *  *     *  * * ** **  * = *   *  * *  x2);
* * ** * * *******       ***  if roots are not real
*  *   ***  * * ** *** ***  **
*  ******  *     **** **** * ***
 ***   *   **    ** *  **      *** ** * * ***** *  * * ***** * *  ** = -b/(2*a);
** * ** **  *****   *******   ***  * *** ** *  *    * *** *  * = ****     * 
*    *   ******** *** *  * *    * ** *  *   * *** *****  * * ** *** * of %.2fx^2 + %.2fx + %.2f = 0 are complex and  **    * **  *  a,b,c);
* *  **  **** *    * * ** *  * **       * *  * * *      ***     * *** = ****  **  *   realPart,  ****   
 *  * **** *    * **** *** ** *  * * * **  *  *   * * **      *  = **  **** *   realPart, * *   * ** **
  * *   *  ******* **  *

 * ***** * ** * * ****  * *  * 0;
}

answered Nov 9, 2017 by 112233 (-167 points)

112233 · Answer 2 · 2017-11-09 17:17:35

Hidden content!
#include ***  * **** *  
#include  ********* *

int main()
{
* ** * ****** * * *   * **     ** a, b, c, determinant, x1,x2, realPart,  ** *  * 


  ** *  *   *  * **  * ** ***** *   *   ** * %lf ***  *   **   * **  &b, &c);


   *****  ** **  * * **    ** *   *   * = b*b-4*a*c;

** ** ** ****  *  ** *** ** *   condition for real and different roots
*** ****  *   **  ** **  * *     (determinant > 0)
**** * *  **** *   * * **  
* *  **       * *** *  ** sqrt() function returns square root
  * ** ****** *   ***  * **   * **    *    **** **  =  **** ** ** * *    
** * ***  *  *  *  *   ****** ** **** * *     * *  = ** *** *  ***  * * ***

 ** ***  **   **  **** **    ** *    *   *  ** *     *  *  ** * * * * of %.2fx^2 + %.2fx + %.2f = 0 are real and ***** ** *   * **** **
   *  * ***     ** **  *    *       * ** *    *    ****** *  *  *** *  =  *  ** *  x1);
    **********  *  *  ****** *     * *  **  ** *      ** ****   ** ** *  =     * *   x2);
*** *  * * ** *  * * ***** 

 **    *  ** * ** *    ***  * ** ** ** for real and equal roots
 *      ***   *   *  *  **  ** if (determinant == 0)
  *  **   ****   *           
**   **** * *  * * **** *    ***** *  *    *  * * *** = x2 = -b/(2*a);
**  *   *  *   *    ***  ***   ** **        **  *     **  ***   *      ** of %.2fx^2 + %.2fx + %.2f = 0 are real and *    * **  ** a,b,c);
 ***  ******  ***     *  *** *   *    ** * *  ** *** *  *** * *    * = x2 =   *  ** x1);
 ** **  ** * *** *  *  * *

* ***  *   * *   * * if roots are not real
 ***     *     *   ***  * * **
 ***** ****  * **   ** * ** **
  * * *****  *** *       * ** *     *** ****   * *  *   = -b/(2*a);
* *  *    *  ** *   ** *   **  **  ** ****** *** ** ****   =   ** **    * *  **
* ** *  **  **  ** *   *  **    * **  * **    **    ** **    * ****    * * of %.2fx^2 + %.2fx + %.2f = 0 are complex and ** ** ***   **     a,b,c);
**** *** *  ******** *   *  *     ** *** *    *  * * * * * * ** =  ** ***  ** ** * realPart,  *   **
*** * * ** *****  **   *  * ** ** **** *  ** * ** *   ***  ** *  ** =  * * **   * **** realPart, ***    * ****
 **** ** **    ****** * 

    *** ** *  **    ****   0;
}

answered Nov 9, 2017 by 112233 (-167 points)

garrylin2 · Answer 3 · 2017-11-02 19:54:55

Hidden content!
  * ***  ***  * **  * *
 ** ** * * *  * *   **
int main(void)
{
 *  * **       ***  **** **  *****  a,b,c,d;
  **** ***   *   ***   ***    **  ****   %f **  *********   *   **  *  ** * 
**  **  **  *  * *  * *  *  * 
 * ****  ***   * **   * *  *  *** *** 
*   * * **** *     * ** * ** ** ** * **** *  ****  ** *** *  * *   ***  of %.2fx^2 + %.2fx + %.2f = 0 are real and  *  *** = %.2f\nx2 = * ** *  **  ** +        *  *  - *   *    **
 *  *  **   ** *     *    *
     * *** *** **  *  *  *** (d==0){
 * **   *********   * *   *   ****** **** ** *****    **   **  **  of %.2fx^2 + %.2fx + %.2f = 0 are real and same\nx1 = x2 = **** * ****   *  + ** * **    
*    **   *** * **  ***  *  *
* * **  * *    ****  ** ***  (d<0) {
* *    *    ******** * * ** *** **  *  * *     *   **** *   *** * * ** of %.2fx^2 + %.2fx + %.2f = 0 are complex and **     =  *  **** =   ** ** * * **  **  *  * * * ***** * * *  *  ** *
  **  **   ******* *   ***
}

answered Nov 2, 2017 by garrylin2 (-204 points)

garrylin2 · Answer 4 · 2017-11-02 19:53:31

Hidden content!
* ****  **    * * *  **  
* * *   *  * * ** 
int main(void)
{
***  * *  **** * * * * ** *** a,b,c,d;
  ***** **** **    ***     * *** * *    %f    *  *** *  *****  * * * **** 
 *** *** *    *     **  ** * *  * * ***
  * ** ***    **  *   *   *** * (d>0){
   *  *   * ** * * *** ***  ** **  *  **  **  *** *  * * *   * * ** **   of %.2fx^2 + %.2fx + %.2f = 0 are real and  ** ***** = %.2f\nx2 =  *  ** **     *   + * *  ****  -  *  *  **
  *  *  **** ** **  *****   
* ********** *  *  *** **  *** (d==0){
* * ******* ***** * *   ** ** ***  *      ** * **  *** **  *  *  ** * of %.2fx^2 + %.2fx + %.2f = 0 are real and same\nx1 = x2 =  * *  * *  +    ***   
**** * * *********      ** *
*   *** *** * ****  * ** *   * *** {
  ** **   **** **     *  ****   ***    * * ** ** *  ****    * * * * of %.2fx^2 + %.2fx + %.2f = 0 are complex and * **  = **  *** ** = *** **** *****         * * * ** * ** **  ** **
 * ** *  *   *    *     *** 
}

answered Nov 2, 2017 by garrylin2 (-204 points)

rick · Answer 5 · 2017-11-02 19:34:07

prog.c: In function 'main':
prog.c:5:5: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
     scanf("%f %f %f",&a,&b,&c);
     ^~~~~
prog.c:5:5: warning: incompatible implicit declaration of built-in function 'scanf'
prog.c:5:5: note: include '<stdio.h>' or provide a declaration of 'scanf'
prog.c:13:9: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
         printf("Roots of %.2fx^2 + %.2fx + %.2f = 0 are real and different\nx1=%.2f\nx2=%.2f\n",a,b,c,x1,x2);
         ^~~~~~
prog.c:13:9: warning: incompatible implicit declaration of built-in function 'printf'
prog.c:13:9: note: include '<stdio.h>' or provide a declaration of 'printf'
prog.c:17:9: warning: incompatible implicit declaration of built-in function 'printf'
         printf("Roots of %.2fx^2 + %.2fx + %.2f = 0 are real and same\nx1 = x2 = %.2f",a,b,c,x1);
         ^~~~~~
prog.c:17:9: note: include '<stdio.h>' or provide a declaration of 'printf'
prog.c:21:9: warning: incompatible implicit declaration of built-in function 'printf'
         printf("Roots of %.2fx^2 + %.2fx + %.2f = 0 are complex and different\nx1 = %.2f+%.2fi\nx2 = %.2f-%.2fi",a,b,c,x3,x4,x3,x4);
         ^~~~~~
prog.c:21:9: note: include '<stdio.h>' or provide a declaration of 'printf'

rick · Answer 6 · 2017-11-02 19:28:09

Hidden content!
#include<stdio.h>
#include<math.h>
int main()
{
  ****    ****   **  *** a,b,c,d,x1,x2,x3,x4;
 *    ***** * * *** ** ** *    ** %f  **   *  ****  **    *  * *     
 ******* * *** *** *** * *       
 * **    *  **  *  ***  ** *   * *  **  ***
   *      * *  * *       * **** *    **
  *    **    *       ***  * *    *    
 *  *  * **** ****      **  * *
**           * **   **  * * **  * ** ** * *  * * **
 * ****     *  ** **  *   **   
**   * *  * ***   *  * * **  **   ****** **    ** *    * ***** ** ****  **  of %.2fx^2 + %.2fx + %.2f = 0 are real and  **  * * * ********      *      **** ****   
*  *  * ** * *** ** *  **   
* ***  *** *** *   ** * * * **  * * **  ****** * * 
   *  ****  *  **   ******* **  
     *  *  ****   ****          *      ***** ** ** *   *  ***  ** of %.2fx^2 + %.2fx + %.2f = 0 are real and same\nx1 = x2 = %.2f",a,b,c,x1);
 * * *****  **  * *  ** **
* ** *  ** *  *   ** *  * *   *    *      **             ** *  
** *      *  ***  ** *     * *
 **  ******  * ** *  *  * ***   ** * ** *   *  * *   **     ** *  of %.2fx^2 + %.2fx + %.2f = 0 are complex and different\nx1 = %.2f + %.2fi\nx2 = %.2f - ****  *   * * *  **   *
  * ***       **    ***
 * ****  *   * *** *      *  *  0;
}